An intake valve or an exhaust valve of an internal combustion engine is driven so as to be opened and closed by a power taken out from a crank shaft of the internal combustion engine. In recent years, it is tried to drive so as to open and close the intake valve or the exhaust valve by an electric motor. For example, there has been proposed a valve gear which opens and closes the intake valve by rotating a cam shaft by stepping motor (Japanese Patent Application Laid-Open (JP-A) No. 8-177536). In addition, there is JP-A No. 59-68509 as a prior technical document relevant to the present invention.
In a valve drive using an electric motor, since it is possible to drive a cam separately from a rotating speed or a rotating direction of the crank shaft of the internal combustion engine, a freedom of control is high, and it is possible to achieve a valve gear characteristic which cannot been obtained by the conventional mechanical valve gear. However, a specific control method suitable for improving a performance such as an improvement of response has not been clarified.